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I also noticed the refrigerant drum is marked R-22, I have checked with my colleague, he said the drums had been cleaned and evacuated, from the current operation record, I don't think the chiller has any mix of R-22.
Yesterday I did the rotor bar test with a variac, 110VAC input, 0-130VAC output, 10A,
I adjust the output amps to 9.7(read by a analog clamp ammeter), then I rotate the motor shaft slowly, the amp reading swing from 9.1 to 10.1, since the variation is not so significant, I am not sure the rotor bar can be determined to be defective.
Tomorrow I am going to test it again with a portable electric welding machine, with a higher input current, maybe it will be clearer to identify the problem

Taicool, I have never heard of using a portable welding machine for that purpose. I would not do that. Even if I saw someone else do that with no apparent problem, I would still not do that. It has been several years since I've performed an open rotor test, and I don't recall what numbers to look for. If you were using an approved, published procedure (I hope you were), then it should have the numbers to look for. And that should indicate if the rotor is acceptible or not. Please don't follow the wrong path in your troubleshooting simply because it is more interesting.

That 1 amp. deviation is far more than 5% and you my friend have an open rotor bar....Period
To take a look at which one is actually the culprit, have your trusty motor shop put a "Growler" test on the rotor, then with a hack-saw blade placed over each segment of iron(one at a time) and watch the hach-saw blade do a dance when you are next to the rotor bar that has opened up.
I do not know how much fluctuation you were expecting in the applied current, but a good rotor will have almost no detectable deviation at all,,,
Lastly....What kind of "Welding Machine" are you going to use that will put out more than the 130 volt A/C that your newly purchased Variac puts out??

Thankee' Billy..I been waiyng on Taicool to post his findings.
Now...If we can just get Moparmyway to let us know what the hell was wrong with his "Speed-Changing" motor, the all will be well in the universe.

side bands occur due to vibration amplitude modulation (changes in vibration amplitude or 'quantity')

if the side bands are spaced at pole pass frequency, then open rotor bars are suspected (especially if you can see them on the vibration spectrum!)

while a 'failed' variac reading indicates an open rotor bar, you may still have a rotor bar issue. a rotor bar with a high resistance joint might show that it is ok, but after it heats up, you can get a rotor bar issue.

vibration analysis will show it while the motor is under load. a rotor bar vibration will show up as a greater vibration at greater loads and less vibration at lower loads. the motor speed will also respond accordingly. higher speeds at lower loads and lower speeds at higher loads.

Thankee' Billy..I been waiyng on Taicool to post his findings.
Now...If we can just get Moparmyway to let us know what the hell was wrong with his "Speed-Changing" motor, the all will be well in the universe.

This has been an interesting, and informative, thread. I too have been watching Moparmyway's thread. Looking forward to seeing how it ends.

Good evening, Gentlemen;
Yesterday I kept fighting with this onerous chiller for a whole day,below are those moves I have carried out,
1. I tested the rotor with variac again, the variation is about 0.35 amps(when the first time I did it two days ago, I think I have misread the reading, for one division on the analog clamp-on ammeter, it is only 0.5amps, I apoligize for the mistake!),
2. measure the motor vibration, the result is as attached,
3. run the motor with coupling disconnected to the compressor, the amp reading on the analog ammeter is pretty stable, the needle swing slightly, I have to keep staring at it carefully to find the motion, while on chiller's control panel, the FLA% jump about between 24%-25%,
So far I am still inclined to believe the problem is caused by an open rotor, just not 100%.

Next step for me to do is to ask a motor shop to help on confirm the rotor problem as they are professional and they have some precision instruments for a good test.

That sounds like a good idea, Taicool. By the way, the first open rotor test I was involved in, I went along with an older, more experienced technician. I was basically a trainee. I hate to think how lost I would have been on my own for the first one. Don't forget to keep us updated. Billy.

I saw that post where Moparmyway mentioned he borrowed your tools. I thought to myself "aha, a clue as to who, and where, the mysterious Jayguy is". And then, dang it Jay, you went and changed your secret identity!